The invention herein described relates generally to an energy-absorbing filter for a motor, and more particularly to a phase current compensation filter for reducing the mechanical position settling time of a hybrid step motor. The energy-absorbing filter may have other applications, particularly where the mechanical oscillations of a motor can be reduced by the inclusion of a large capacitance.
Motors are used in numerous fields including disk controllers, robotics, integrated circuit fabrication and many others. A typical motor causes movement in response to a command voltage or current. Oscillation about the desired position occurs when the motor nears the desired position. The size and duration of the oscillation are determined according to the characteristics of the motor such as damping. Clearly it is desirable to have this oscillation decay as rapidly as possible. However, minimizing the settling time of the oscillation decay may require a tradeoff in another area of motor performance such as motor efficiency or speed. Thus, a need exists in the motor art for a method or device to decrease motor settling time while maintaining or not significantly degrading the other motor characteristics.
The present invention provides an energy-absorbing filter technique for reducing mechanical motor oscillations by providing a large capacitance in parallel to the motor windings so as to cause the motor oscillations to be dissipated as resistive losses. Specifically, the energy-absorbing filter is used to provide a particular capacitance across a motor winding such that a virtual shunt is created. The virtual shunt causes the mechanical oscillations of the motor to be dissipated as resistive losses rather than being returned to the windings. This quickly damps the oscillations thereby reducing the settling time of the motor.
According to one aspect of the present invention, an energy-absorbing filter couples a capacitance to a winding of a motor to damp mechanical oscillations of the motor at the end of a move.
According to another aspect of the present invention, an energy-absorbing filter couples a capacitance to a winding of a motor to damp mechanical oscillations of the motor wherein an equivalent impedance of the energy-absorbing filter coupled with the motor is a substantially resistive.
In an embodiment, the motor may be a hybrid step motor and the filter may include a transconductance amplifier. In an embodiment, the filter may provide a shunt capacitance across the motor winding such that the mechanical oscillations are dissipated as resistive losses. The combined impedance of the filter and the motor are a substantially real resistance during the settling of the motor.
In an embodiment, the filter includes a positive resistive element, a negative resistive element, a complex impedance element, two amplifiers and a current sensor. The values of the resistors and the complex impedance element may be selected according to the electrical system parameters of the motor.
In an embodiment, the filter may be an ideal current regulator.
In an embodiment, the filter is one of a digital, analog, hybrid or software filter. In an embodiment, the filter reduces the settling time of the motor.
According to another aspect of the present invention, a method comprises measuring the electrical parameters of a motor, and setting the parameters of an energy-absorbing filter according to the electrical parameters of the motor such that the energy-absorbing filter reduces the mechanical oscillations of the motor at the end of a move.
In an embodiment, the energy-absorbing filter is a software filter.
In an embodiment, the parameters of the energy-absorbing filter are independent of motor inertia and motor load.
According to another aspect of the present invention, a method comprises including an energy-absorbing filter having filter characteristics with a motor having mechanical and electrical characteristics and selecting the filter characteristics such that an equivalent impedance of the motor and the energy-absorbing filter combined is substantially a purely resistive impedance.
In an embodiment, the filter characteristics may be selected according to the electrical characteristics of the motor. In an embodiment, the motor is a step motor. In an embodiment, the filter may be a digital, analog, hybrid or software filter. In an embodiment, the filter includes a transconductance amplifier. In an embodiment, the filter reduces the settling time of the motor.